hermes - 💡(How to fix) Fix [Feature]: Support Telegram document thumbnails in send_message [1 pull requests]

Problem or Use Case

Hermes can send files to Telegram via send_message using MEDIA:/absolute/path, but there was no way to provide Telegram Bot API sendDocument.thumbnail for document attachments such as PDFs. This makes PDF/document sends look less polished in Telegram clients when a preview image is available.

This came up while validating Telegram document delivery from the gateway: a PDF sent successfully, and the desired behavior is to let callers attach an explicit preview image.

Proposed Solution

Add a lightweight message directive for Telegram document attachments:

[[thumbnail:/tmp/preview.jpg]]
MEDIA:/tmp/report.pdf

The directive should be stripped from the visible message and forwarded to Telegram's sendDocument.thumbnail parameter when the media attachment is sent as a document. It should support quoted paths for filenames with spaces.

Implementation scope:

• Add thumbnail_path support to the platform adapter document send API.
• Pass thumbnail_path through the Telegram adapter to bot.send_document(thumbnail=...).
• Teach the send_message tool to parse and strip [[thumbnail:...]] directives.
• Add regression tests for adapter-level and send_message-level flows.

Alternatives Considered

• Auto-generating thumbnails for every PDF: useful later, but larger in scope and more opinionated.
• Adding a separate thumbnail argument to the public send_message schema: clearer for programmatic callers, but awkward for the existing text-plus-MEDIA: messaging pattern.
• Encoding thumbnail metadata into the MEDIA: tag: less readable and harder to document.

Feature Type

Gateway / messaging improvement

Scope

Medium (few files, < 300 lines)

Contribution

I'd like to implement this myself and submit a PR.

Validation Notes

Manual validation was performed by sending a PDF with a generated JPEG thumbnail through Telegram; the send result was successful.